Beaufort Wind Scale Beaufort Wind Scale Developed in 1805 by Sir Francis Beaufort, U.K. Royal Navy Force Sea surface smooth and mirror-like Calm, smoke rises vertically Scaly ripples, no foam crests Smoke drift indicates wind direction, still wind vanes 2 Small wavelets, crests glassy, no breaking Wind felt on face, leaves rustle, vanes begin to move 3 Large wavelets, crests begin to break, scattered whitecaps Leaves and small twigs constantly moving, light flags extended 4 Small waves 1-4 ft.

becoming longer, numerous whitecaps Dust, leaves, and loose paper lifted, small tree branches move 5 Moderate waves 4-8 ft taking longer form, many whitecaps, some spray Small trees in leaf begin to sway 6 Larger waves 8-13 ft, whitecaps common, more spray Larger tree branches moving, whistling in wires 7 Sea heaps up, waves 13-19 ft, white foam streaks off breakers Whole trees moving, resistance felt walking against wind 8 34-40 Gale Moderately high (18-25 ft) waves of greater length, edges of crests begin to break into spindrift, foam blown in streaks Twigs breaking off trees, generally impedes progress 9 41-47 Strong Gale High waves (23-32 ft), sea begins to roll, dense streaks of foam, spray may reduce visibility Slight structural damage occurs, slate blows off roofs 10 48-55 Storm Very high waves (29-41 ft) with overhanging crests, sea white with densely blown foam, heavy rolling, lowered visibility Seldom experienced on land, trees broken or uprooted, "consider

able structural damage" 11 Beaufort wind scales Beaufort wind scales The best known scale for wind speed is that of Sir Francis Beaufort (1774–1857), a captain in the British Admiralty who drew up the first version in 1806 for his own use.

Ordered lists of wind names have been made for millenia (everyone knows a hurricane is stronger than a breeze, for example). Quantifying wind velocity was a later development. Smeaton One of the first to do so was the English engineer John Smeaton, who was interested in windmills¹ and built a device for measuring the effectiveness of windmill sails at different wind velocities. His wind scale ran from 1 to 8, describing each force by what he observed at a particular windmill, the Austhorpe Mill near his home. For example, number 2, Breeze, was "Sufficient to move the branches of trees, and Mill from 6 to 9 turns" per minute, while at number 5, Very Fresh, "Wind growing noisy, and considerable agitation of Trees, Mill 18 [turns per minute] to ¾ Cloth." Smeaton's scale caught the attention of the Hydrographer to the British Admiralty, Alexander Dalrymple. The Hydrographer was the person in charge of gathering data and issuing charts, and a convenient, consistent way of noting wind speed would be invaluable to the navy.

Dalrymple changed the scale to 0 to 12, from Smeaton's 1 to 8, and changed the wind names to those usually used in ships' logs. And he brought his scale to the attention of Captain Beaufort, who had distinguished himself by producing meticulous records. The genius of Beaufort's addition to the scale was that he defined each name and number by a description of the maximum amount of sail a man-of-war could carry under those wind conditions. Force Hurricane Or that which no canvas could withstand. Notice that this scale depends on observation of a ship of a particular class sailing into the wind (“clean full”), and. for force numbers 5 through 9, on such a ship being in pursuit of an enemy vessel.3 This specificity was not much of a problem. Men-of-war were fairly standardized; any sailor familiar with them (and most were) could observe sails and assign a Beaufort number, and conversely, given a Beaufort force number, a sailor could picture wind conditions. Blair Kinsman suggests that one value of the scale to the Admiralty was that it facilitated courts-martial of captains who failed to pursue with all possible vigor.

In 1829 Beaufort was promoted to Hydrographer. According to Scott Huler , the first official use of the Beaufort scale occurred in 1831 when Beaufort directed it be used on the second voyage of the Beagle, the expedition that took Charles Darwin to the Galapagos (Beaufort had recommended him for the job). On 28 December 1838, the Admiralty formally adopted Beaufort's scale for “all Her Majesty's Ships and Vessels of War.” In August 1853, representatives of ten nations met in Brussels (the First International Meteorological Conference). One of their goals was to agree upon a standard format for the weather observations in ships' logbooks; the scale they adopted for the wind was Beaufort's. In 1862, the British Board of Trade adopted the scale for commercial vessels. When the International Meteorological Organization was formed (Vienna, 1873), it continued its predecessor's use of the Beaufort scale.

Beaufort wind scale on land In the last quarter of the 19th century numerous investigations were made with the goal of assigning a range of wind speeds to each of Beaufort's numbers. The British Meteorological Office was active in this work and in 1906 published a report with wind speed ranges. This report also introduced descriptions of what would be observed on land at each Beaufort number. Huler has made a fairly convincing case that the principal author of the Land Criteria was the “North Shields observer,” one George Clark, head clerk at the North Shields Post Office. Force Wind speed changes with height. In June, 1939 the International Meteorological Committee adopted a correlation with wind speeds measured at a height of 6 meters. Great Britain and the United States, however, had already standardized on measuring the wind speed at 11 meters above ground level, which is shown in column 2 below, in miles per hour. Beaufort wind scale for the open sea The replacement of sailing vessels by steam- and petroleum-powered engines made Beaufort's descriptions of sails obsolete. Instead of observing sails, sailors turned to observing the sea itself: waves, spray, froth, white caps, and so forth.

Here it is necessary to distinguish between what sailors call the "sea" and swells. Swells are disturbances of the sea surface due to wind that blew many miles away, sometimes thousands of miles away. Swells have rounded crests. "Sea" is the effect of local wind. In 1927 P. Petersen, a German sea captain, published a scale5 from 0 to 12 for the state-of-the-sea. In this he drew upon earlier shipboard measurements6 with anemometers. Today's state-of-the-sea descriptions remain largely translations from Petersen's German, and the scale is sometimes called the Petersen state-of-the-sea scale. The scale, however, remains Beaufort's, in the sense that the numbers and correlated wind speeds remain the same. A version currently used by mariners is shown below. Please refer to the warnings following the table. Column 2 is the range of wind speeds in knots, measured at a height of 33 feet above sea level. Column 5 is the probable height of waves in feet in the open sea, remote from land. In enclosed waters, or when near land with an offshore wind, wave heights will be smaller and the waves steeper.

Column 6 is the probable maximum wave height in feet in the open sea (the caveats for column 5 apply here as well) Force Estimating wind force by the sea criteria is difficult at night. An increase of wind does not immediately produce an increase of sea. Fetch, depth, swell, heavy rain, floating ice and tide effects should be considered when estimating the wind force from the appearance of the sea. WARNING: For a given wind force, sea conditions can be more dangerous near land than in the open sea. In many tidal waters wave heights are liable to increase considerably in a matter of minutes. In presenting a very similar table, the World Meterological Organization warns: “This table is only intended as a guide to show roughly what may be expected in the open sea, remote from land. It should never be used in the reverse way, i.e., for logging or reporting the state of the sea.”7 1. John Smeaton. Experimental Enquiry concerning the Natural Powers of Wind and Water to Turn Mills and Other Machines Depending on a Circular Motion. And An experimental examination of the quantity and proportion of mechanic power necessary to be employed in giving different degrees of velocity to heavy bodies from a state of rest.

Also new fundamental experiments upon the collision of bodies. With five plates of machines. London: Printed for I. and J. Taylor, 1794. The first edition was published in 1760. Smeaton also included a table relating wind names to velocities in miles per hour and feet per second,and force on a foot-square board. Smeaton attributed the table to his friend Thomas Rouse, an amateur scientist. Austhorpe Mill, near Leeds, "was situated in Austhorpe Lane, at the top of what was known as Appleyard's Hill. A brick-built tower, it is remembered as just a ruined shell in 1928. The site is now the school playground of Austhorpe Primary School." ( accessed 17 Sept 2006) 2. Alexander Dalrymple. Never published. Two printer's proofs exist. 3. This paragraph is greatly indebted to two articles by Blair Kinsman. Historical Notes on the Original Beaufort Scale. The Marine Observer, vol. 39, pages 116-124.

(1969) Another article by Professor Kinsman covers much of the same ground in a more popular style: Who Put the Wind Speeds in Admiral Beaufort's Force Scale? Oceans, vol. 2 no. 2. He is also the author of the following, which we have not seen. An exploration of the origin and persistence of the Beaufort wind force scale. Technical Report, Chesapeake Bay Institute #39. Annapolis : Chesapeake Bay Institute, 1968. 4. Sir William Napier Shaw and Sir George Clarke Simpson. The Beaufort Scale of Wind-Force. Report of the Director of the Meteorological Office (W. N. Shaw) upon an inquiry into the relation between the estimates of wind-force according to Admiral Beaufort's scale and the velocities recorded by anemometers belonging to the Office, with a report upon certain points in connection with the inquiry by G. C. Simpson ... and notes by Sir G. H. Darwin...W. H. Dines and Commander Campbell Mepworth. Official Publication No. 180. London: The Meteorological Office, 1906. 5. P. Petersen.

Zur Bestimmung der Windstärke auf See. Für Segler, Dampfer und Luftfahrzeige. Annalen der Hydrographie und Maritimen Meteorologie. March 1927, pages 69-72. 6. Prager. Annalen der Hydrographie und Maritimen Meteorologie. 1905, pages 1-. 7. World Meteorological Organization. Manual on Codes. International Codes. Vol. I.1 (Annex II to WMO Technical Regulations). WMO-No.306. Defining the Wind. The Beaufort Scale, and How a Nineteenth-Century Admiral Turned Science into Poetry. New York: Crown, 2004. A writer with a passionate interest in Beaufort's scale details his research into its origins. Includes an extensive bibliography. A number of maritime nations issue illustrated state-of-the-sea guides, such as: State of Sea Booklet. Bracknell, England: National Meteorological Library. U.S. Dept. of Commerce. National Oceanic and Atmospheric Administration. Guide to Sea State, Wind and Clouds. Washington (?).

No date or publication information in the publication, but circa 1995. SuDoc Number is C55.8:SE 1 W. T. R. Allen. Wind and sea: State of sea photographs for the Beaufort wind scale. Environment Canada, Atmospheric Environment Service, 1983.

Beaufort Wind Scale Beaufort Wind Scale Devised by British Rear-Admiral, Sir Francis Beaufort in 1805 based on observations of the effects of the wind Beaufort Effects observed on the sea Effects observed on land Sea is like a mirror 1 Ripples with appearance of scales; no foam crests 2 Small wavelets; crests of glassy appearance, not breaking 3 Large wavelets; crests begin to break; scattered whitecaps 4 Small waves, becoming longer; numerous whitecaps 5 Moderate waves, taking longer form; many whitecaps; some spray 6 Larger waves forming; whitecaps everywhere; more spray 7 Sea heaps up; white foam from breaking waves begins to be blown in streaks 8 18-25 Gale Moderately high waves of greater length; edges of crests begin to break into spindrift; foam is blown in well-marked streaks 9 23-32 Strong gale High waves; sea begins to roll; dense streaks of foam; spray may begin to reduce visibility 10 29-41 Storm Very high waves with overhanging crests; sea takes white appearance as foam is blown in very dense

 streaks; rolling is heavy and visibility is reduced 11 Exceptionally high waves; sea covered with white foam patches; visibility further reduced 12 Air filled with foam; sea completely white with driving spray; visibility greatly reduced * World Meteorological Organization Fujita Scale of Tornado Intensity STORMFAX and the STORMFAX logos are registered trademarks in the United States and Canada Please read our Legal Notice and our Privacy Statement.

©1996-2017 STORMFAX Beaufort Series | Article about Beaufort Series by The Free Dictionary Beaufort Series | Article about Beaufort Series by The Free Dictionary Also found in: Dictionary , Thesaurus , Wikipedia . Beaufort scale, a scale of wind wind, flow of air relative to the earth's surface. A wind is named according to the point of the compass from which it blows, e.g., a wind blowing from the north is a north wind. ..... Click the link for more information. velocity devised (c.1805) by Admiral Sir Francis Beaufort of the British navy. An adaptation of Beaufort's scale is used by the U.S. National Weather Service; it employs a scale from 0 to 12, representing calm, light air, light breeze, gentle breeze, moderate breeze, fresh breeze, strong breeze, moderate gale, fresh gale, strong gale, whole gale, storm, hurricane.

Zero (calm) is a wind velocity of less than 1 mi (1.6 km) per hr, and 12 (hurricane) represents a velocity of more than 74 mi (119 km) per hr. Beaufort's original scale was later correlated to wind speed in two different ways. The U.S. and British scale is for winds measured at a 36-ft elevation, while the international scale requires only a 20-ft elevation. The Beaufort scale is the oldest method of judging wind force. Separate scales for tornadoes and hurricanes did not come until the 1970s. The Fujita scale Fujita scale or F-Scale, scale for rating the severity of tornadoes as a measure of the damage they cause, devised in 1951 by the Japanese-American meteorologist Tetsuya (Ted) Fujita (1920–98). ..... Click the link for more information. for tornadoes was proposed in 1971 by Tetsuya (Ted) Fujita; in 2007 the Enhanced Fujita scale, incorporating improved knowledge of wind destruction, as was adopted.

Soon after the development of the Fujita scale the Saffir-Simpson scale Saffir-Simpson scale , standard scale for rating the severity of hurricanes as a measure of the damage they cause; it is based on observations of numerous North Atlantic Basin hurricanes. ..... Click the link for more information. for hurricanes was formulated by Herbert Saffir and Robert Simpson. Bibliography These values refer to well-developed wind waves of the open sea. The lag effect between the wind getting up and the sea increasing should be borne in mind. The official term is Strong gale, however, the Met Office uses the descriptive term Severe gale To convert knots to mph multiply by 1.15, for m/s multiply by 0.514. Last updated: Mar 3, 2016 5:35 PM SSSS Clubhouse : Beaufort Scale Moderate longer waves. better formed, many whitecaps, much foam, some spray 3-4 ft The Race Committee should observe sea conditions at the start during and at the finish of the race, and determine an average Beaufort Number for that race.

Round off knots to nearest whole number or MPH to nearest tenth to determine Beaufort Number if anemometer is used. Care should be taken in observing that wind strength approximates that of the race course. Wave height is dependent on water depth and length of time that the wind has been blowing. These are typical heights for lakes, bays, and estuaries. The above conditions and wave heights should prevail after the times indicated. Don't neglect the effect of large numbers of powerboats on enclosed bodies of water in estimating wave heights. The Beaufort, Saffir-Simpson, & Fujita Scales That which no canvas could withstand. hurricane No sail can stand even when running The Beaufort Scale has become the standard method of judging wind force. It is not the oldest, since rating the strength of wind by number and/or assigning names to the ratings had been done for some time. In 1806 Francis Beaufort (later Admiral and Sir) wrote out a numerical scale in his log. This was evidently copied from a British Admiralty pamphlet. Beaufort, however, refined and specified the scale, and in 1838 it was officially adopted by the Admiralty.

In 1906 a report further refined the scale with corresponding wind speeds and descriptions of effects on land. Beaufort himself had specified the sailing conditions that went with each rating, as seen in the chart at right. Separate wind scales for tornadoes and hurricanes did not come until the 1970's. The Fujita (or Fujita-Pearson) Scale for tornadoes was proposed in 1971 by T. Theodore Fujita and Allen Pearson. Soon thereafter, the Saffir-Simpson Scale for hurricanes was formulated by Herbert Saffir and Robert Simpson. Thus, the movie Twister was anachronistic when it had Helen Hunt's father warn, in 1965, that they might have an F5 tornado headed toward them. The scale had not been invented yet. There has been some recent revision of some of these systems. I have not yet updated the presentation here. The complete Beaufort Scale has thirteen divisions, as shown above (starting with zero ). Beaufort grouped these into 5 categories of winds, or finely divided using five "breezes," four "gales," and four other designations.

light strong whole Breezes and gales both use the same simple scale of adjectives in the table at left. It always seemed a little odd to me that the designations jumped directly from "breezes" to "gales." One might expect an intermediate category, like simple "winds." Indeed, Beaufort himself grouped "strong breeze" and "moderate gale" as "strong winds" [ note ]. The Fujita and Saffir-Simpson scales are almost entirely subdivisions of hurricane force winds. Only the F0 tornado merely has gale force winds. The complete table below gives wind speeds, the appearance of objects affected by the wind (as described in 1906), the kinds of damage to be expected from tornadoes and hurricanes, and other details, like barometric pressure, for hurricanes. Gale force winds mean that a "tropical depression" becomes a "tropical storm," which is then given a name by the appropriate authorities. Warning flags for water craft are also given. At the left of the table, the Beaufort, Fujita, and Saffir-Simpson Scales are given B, F, and S numbers, respectively.

Note that severe hurricanes are often attended with tornadoes as well. Hurricanes in the Western Pacific are called "Typhoons," and those in the Indian Ocean, "Cyclones." Tornadoes used to often be called "Cyclones" also. Modern terminology is that all low pressures systems, which includes hurricanes, tornadoes, and less severe phenomena, are "cyclones." In 1927, a German captain, Petersen, provided "State-of-Sea" descriptions for each wind force. These are given at right. The term "white horses" is not familiar to me, at least from American usage. This seems to mean simply "whitecaps." B0 261-318 mph strongly built homes are completely blown away My introduction to meteorology came with the Life Science Library book Weather, by Philip D. Thompson, Robert O'Brien, and "the Editors of LIFE" [Time Incorported, 1965], which I acquired, about the time it was published, when I was in Junior High School. Some of the descriptions here are still drawn from that volume.

I did have an actual meterology class at the University of New Mexico in 1968, but I got less out of it than I might have and failed to hold on to any class materials. Now, however, complete background to all of this can be found at The Weather Channel website. The following descriptions have been taken from that source, from Everything Weather, The Weather Channel's CD-ROM, and from other sources, web and print, that I have lost track of. A detailed history of the Beaufort Scale is now to be found in Defining the Wind, The Beaufort Scale, and How a 19th-Century Admiral Turned Science into Poetry by Scott Huler [Three Rivers Press, New York, 2004]. I was unaware of the sailing condition descriptions, or indeed of the history of the Scale, until finding this book. The Petersen State-of-Sea descriptions can be found at the British Met(erological) Office .

12 hurricane It may be silly, but it bugs me that the Beaufort terminology should jump directly from a "breeze" to a "gale." As I use the words, "wind" can refer to all movement of air, but the very same word also denotes something that is rather more than a "breeze" but still less than a "gale." I don't think of a breeze as much of a wind at all, while a gale is something quite strong and unusual, at least on land, or apart from a winter storm. A breeze is pleasant, and will not cause any inconvenience or rearrange any objects, except the lightest. A real wind, however, many be annoying, render some activities unpleasant, and will move some things around, even if only leaves, that will require attention. But then a gale: no outside activities will be pleasant, and the wind can cause some damage. I remedy this with the additions at left. Here we simply would have three "breezes," three "winds," and three "gales." This is how it might be done in Chinese, where many things, like rank, are divided into "high," , "middle" , and "low" , degrees.

I expect that the exclusive use of "breeze" and "gale," without using "wind" for specific forces, might be to avoid ambiguity. In the traditional Beaufort Scale "wind" is not used with two meanings, the general and the specific. That is quite reasonable. My proposal then, would certainly not be for any usage where ambiguity might cause some inconvenience or danger. The table simply represents my intuition about ordinary usage and meaning, that a breeze is not quite a wind, while a gale is much more than just a wind. Return to Text Clouds Clouds are the mountains of the sky. They can, indeed, be taller than any mountains of the earth, reaching up to 40,000 feet or, rarely, even to 60,000 feet, far beyond Everest. On the other hand, they exist on a vastly different time scale. The tallest clouds can develop and disappear in less than a day, while earthly mountains grow and erode over millions of years. In Los Angeles, there is usually not much to be seen in the way of interesting clouds. Much of the weather is simply clear, and in the spring and summer a marine layer of fog and stratus clouds moves in.

Occasionally in the summer, thunderheads develop over the San Gabriel mountains and the storms may, though sometimes not for several years, move over the Los Angeles basin. Winter storms off the Pacific, usually lasting no more than a day or two, are responsible for most of the average rainfall of 15 inches. Growing up in Los Angeles, I didn't feel like I saw much in the way of cloud variety until I lived in New Mexico, Lebanon, Hawaii, and Texas. New Mexico was especially noteworthy for the colors that would play on the clouds: The setting sun could fill the same sky with yellow, pink, orange, and cherry red on different clouds. In Hawaii , where clouds would build up over the windward mountains daily in the rainy season, one striking memory is of the full moon shining on the towering, isolated thunderheads. There was, however, limited thunder from those clouds, which would drop some rain in the valleys and foothills and then disperse, often not even getting Waikiki wet. More violent weather came with the occasional winter storm (a "kona" storm, since the wind may blow from leeward, against the trade winds), or with the rare hurricane. Clouds are classified by form and by altitude.

The basic forms, with symbols, are ("heaped up," in Latin), ("spread out," the neuter form of which is stratum, used for extensive layers of similar rock in geology), and ("lock" or "curl" of hair) . Cumulus clouds tend to form from rising air, from 6,000 feet on up, and so are classified as "vertically developing" clouds. Stratus clouds, below 8,000 feet, may be rather like an elevated fog bank; or, altenatively, fog can be thought of as a stratus cloud at ground level. While cumulus clouds mean that air has risen to an elevation where the temperature is at the dew point , so that the water condenses, with stratus clouds the temperature of the air itself may have fallen to the dew point. Cirrus clouds are ice crystals at high altitude, from 18,000 to 40,000 feet; their whispy structure comes from scattering by the wind.

Besides stratus, low level clouds can include (between 3,000 and 10,000 feet), from which rain falls (nimbus simply means "cloud," or "raincloud") and (below 8,000 feet), where cumulus clouds stretch out in a solid layer, showing a lot more structure than stratus clouds, whose outlines can be very indistinct. At high altitudes (18,000 to 40,000), cirrus clouds can form a fairly solid layer, becoming , or they can take on a lumpy structure, with grains or ripples (a "mackerel sky"), suggestive of cumulus clouds, becoming . At middle altitudes, from 6,000 to 18,000 feet, too low to freeze into cirrus but higher than ordinary stratus, are (above 15,000 feet) and . The "alto-" element is from Latin "altus," which originally meant "grown" but came also to mean "high," as it is used in these names. Altocumulus can be part of the development of cumulus and cumulonimbus clouds.

The highest -- all the way up to 60,000 feet -- most spectacular, and most violent clouds result when the air, rising to form cumulus clouds, continues to rise, drawing moisture to high altitudes and generating extreme conditions. This makes a cumulonimbus cloud. The swelling top spreads out into a characteristic anvil shape, which then may be blown away by high level winds. Because of freezing air at those altitudes, the streaming clouds from the anvil will often take a cirrus form. Freezing air can also cause hail to form, as ice crystals begin to fall and then are lifted back up again and again to grow larger and larger. When the hail finally falls, descriptions of its size are borrowed from the produce counter and from sports: Small hail is described as "pea" sized, whence we move up to "grape" sized, "ping-pong ball" sized, "golf ball" sized, "baseball" sized, and, most devastating of all, "grapefruit" sized. Baseball and grapefruit sized hail can break any window, ruin a car, flatten a field of crops, or even kill somebody.

The movement of wind, water, and ice up and down the column of clouds also generates differentials in electrical charge, which are then discharged as lightning. Isolated thunderstorms, generated by summer heating, may pass over with a minimum of damage. Spring cold fronts, however, pushing still cold air from the north under warm moist Gulf air, as in Texas, can produce massive squall lines of thunderstorms, stretching for hundreds of miles, filling the sky with vast gray clouds, rain, wind, hail, lightning, and, worst of all, tornadoes. These conditions get called, with charming understatement, "severe weather." Short of hurricane force winds, or actual tornadoes, nature provides no more awesome weather. During one overnight thunderstorm and flash flood that I witnessed in Austin, Texas, on the eve of Memorial Day in 1981 , where serious flooding and deaths occurred, the flashes of lightning were so frequent that they were right on top of each other and the night was literally without darkness. I also see other cloud symbols, such as the altostratus plus cirrus symbol at left. I have yet to see exactly what this would look like in the sky, but I like how this looks.

Copyright (c) 1998, 2015 Kelley L. Ross, Ph.D. All Rights Reserved Note on Dew Point The dew point tells us the absolute humidity. The more commonly used "relative humidity" is the percentage to which the air is saturated with moisture. The dew point is simply the temperature at which the air would be saturated, would have 100% relative humidity. Warmer air can hold more moisture, so that air that would be saturated at 75oF, with 100% relative humidity, would only have about 50% relative humidity if the temperature rises to 95oF without any moisture being added. While people complaining of summer humidity often say that both the temperature and the relative humidity must both be 90 or more, this really does not happen and would be deadly if it did. Typical summer dew points in Texas are around 75oF, as in the example just cited. The highest dew point I've ever heard of was 80o, reported by The Weather Channel at places in eastern Pennsylvania and New Jersey as a line of thunderstorms was arriving in June 1998 (I was nearby in New Jersey -- it was humid).

Typical summer dew points in Los Angeles are in the 50's. Extremely humid summer conditions in Los Angeles usually only mean dew points in the 60's. Autumn arrives in Los Angeles in October, when dry air (and sometimes a Santa Ana wind) arrives with the first cold front, dropping the dew point precipitously. October 20, 1996, the dew point in Van Nuys was reported at 37o, the 21st at 14o, and the 22nd at 9o. October 7, 1997, the dew point was reported at 39o and the 15th at 25o. October 5, 1998, the dew point was reported at 13o and the 17th at 19o. Although understanding the dew point in abstraction, its real connection to the feel of the air was not obvious to me until I began seeing dew point isotherm maps on The Weather Channel in the 1980's.

Since air can hold about twice as much moisture for every 20 degrees Fahrenheit, this may be used to write very simple equations for the dew point. In the following equations, D is the dew point in degrees Fahrenheit, T is the air temperature, and H is the relative humidity written as a whole number percentage (i.e. "50" instead of "0.5" for "50%"). The first equation gives the dew point for the temperature and relative humidity, which is usually what one can easily determine, while the second equation gives the relative humidity from the temperature and dew point. D = T - 20*((2 - log H)/log 2) log H = 2 - ((log 2*(T-D))/20) C = 5*(F - 32)/9 C = (5*(F + 40)/9) - 40 F = (9*C/5) + 32 F = (9*(C + 40)/5) - 40 A more precise value for the dew point can be derived from the equations below. For the main equation, the value "X" must be calculated first, based on the relative humidty.

The temperature and dew point here will be in degrees Celsius (or centigrade). Celsius and Fahrenheit can be converted back and forth with the equations in the box at right. (Note that the equations that add and subtract 40, in precisely the same way, may be easier to remember than the more traditional conversion equations.) X = 1 -(.01*H) D = T - (14.55+.114*T)*X - ((2.5+.007*T)*X)3 - (15.9+.117*T)*X14 If we have a temperature of 73oF (22.8oC) at 24% relative humidity, the Fahrenheit equation gives us a dew point of 3l.8oF. The Celsius equation gives us a dew point of 1.1oC, or 34.0oF. An error of 2.2oF, or 1.2oC, is not bad, especially considering how much easier the Fahrenheit equation is to use.

My favorite personal experience with dew point was when I drove from Austin, Texas, to Tularosa, New Mexico, in June 1982. A cold drink in Texas causes a large amount of moisture to condense on a glass. It "sweats"; and the water collects on the table or in a coaster, sometimes so much that it makes it seem like the glass is leaking. Arriving in New Mexico at my aunt and uncle's place, the next day I had a glass of iced tea sitting on the broad arm of a wooden chair. After half an hour, I checked the glass to make sure that there wasn't any condensing water that might damage the wood. There wasn't. At an elevation of over 4000 feet, far from the Gulf Coast, the relative humidity might only have about 5% or so. Copyright (c) 1998 Kelley L. Ross, Ph.D. All Rights Reserved Snow, Sleet, Ice, and Rain The temperatures of the air produce different phenomena of precipitation. The most familiar are snow and rain. In the former, ice crystals fall through air that is below freezing from the clouds to the surface. Snow then accumulates in drifts on the ground.

The water content of snow can vary, so that some times it is dry, light, and fluffy, other times wet, heavy, and dense. Wet snows can adhere, so that drifts can appear to flow or sag without breaking apart. With rain, water droplets fall through air that is above freezing. Puddles accumulate on the ground, or the water flows away. Other forms of precipitation occur when the air temperature changes from above freezing to below between the clouds and the surface. If the boundary occurs high enough, there is time for rain droplets to freeze before hitting the ground. This is sleet. As solid little ice pellets, sleet will tend to fall faster than snow and will hit surfaces with some noise. A snow fall is silent. Sleet can sound like small hail. When it accumulates on the ground, sleet can look a bit like snow, but the consistency and the color will look a bit different. If the boundary between the air above freezing and below freezing is close enough to the surface, we get freezing rain. This is one of the rarer of these phenomena, and its effects are striking and dangerous. Rain drops hit surfaces and freeze.

This produces a glaze of ice on amost anything and a surface of "black" ice on streets. An accumulation of ice becomes heavy. Branches, trees, and power lines can easily be brought down in an ice storm. Driving is treacherous. In the daylight after an ice storm, everything looks like it is wrapped in glass. This can be extraordinarily beautiful, but it may be purchased at a terrible price in damage and even lives. Hail is produced when updrafts carry rain drops high into clouds, and into freezing air at altitude, even during warm times of the year. The rain drop freezes and may fall, or it may be carried up into the clouds again and receive a further coating of ice. This can happen over and over again, producing ever larger hail stones. Hail is thus usually characterized by its size, ranging from pea sized to grapefruit sized. The latter, of course, can cause sever damage or injury when it finally falls to the ground.

Question: Which number on the Beaufort scale denotes a gentle breeze?
Answer: Three